The present invention relates generally to refrigerator controls, and more particularly to an improved refrigerator control which reduces the incidence of abnormal temperature conditions within a refrigerated compartment.
Conventional refrigerator controls have been designed to provide good regulation of compartment temperatures when the refrigerator is operated at room temperatures ranging from approximately 70.degree. F. to 100.degree. F. Recently, the increased use of energy conservation measures, such as household thermostat settings below 70.degree. F. and the use of setback thermostats has resulted in refrigerators being operated in ambient temperatures well below 70.degree. F. This, coupled with improved insulation in modern refrigerators, results in the refrigerator compressor remaining off for long periods of time. During these long compressor-off periods, heat transfer through the divider wall separating the freezer and fresh food compartments, along with convective air flow between the compartments through a return air duct and stratification of air within the fresh food compartment can produce an abnormal temperature condition wherein below-freezing temperatures occur in certain portions of the fresh food compartment. This problem is experienced most often in side-by-side refrigerators, primarily due to the large divider wall area separating the compartments which allows a substantial amount of heat transfer between the freezer and fresh food compartments.
Certain types of food, such as fruits and vegetables, are typically stored in the lower portion of the fresh food compartment, often in a separate "crisper" drawer located in a lower portion of the fresh food compartment adjacent the divider wall separating the fresh food compartment from the freezer. This location has been found to be particularly susceptible to below-freezing temperatures during long compressor off cycles, even though the upper portion of the fresh food compartment may remain at an above-freezing temperature as a result of temperature stratification within the compartment.
Prior attempts to prevent the flow of cold air into the fresh food compartment from the freezer compartment (hereinafter termed "reverse convective air flow") are disclosed in Rivard et al Reissue No. 27,990 and Helsel U.S. Pat. No. 3,375,679. In the Rivard et al reissue patent, a small resistive heater is disposed adjacent the return air duct to set up a current of air which acts in opposition to the cold air flow from the freezer compartment to maintain the desired temperature differential between the freezer compartment and the fresh food compartment during off cycles of the compressor and evaporator fan.
The Helsel patent discloses the use of a flow-responsive check valve which prevents convective air flow through the return air duct during off cycles of the compressor and evaporator fan.
While the above patents disclose apparatus for preventing reverse convective air flow, it has been found that a solution to the problem of reverse convective air flow does not, of itself, provide a reliable solution to the problem of abnormally low temperatures in particular portions of the fresh food compartment.